THURSDAY, May 17 (HealthDay News) -- An international study shows that the cervical cancer vaccine that received government approval in the United States last year also protects women against vulval and vaginal cancers.

The findings seem to confirm that human papillomavirus (HPV), which is responsible for virtually all cases of cervical cancer, is also responsible for many cases of vulval and vaginal cancer. HPV is present in 80 percent of the 6,000 cases of vulval and vaginal cancers diagnosed in the United States each year.

"We've spent a lot of time over the last 20 years trying to show that HPV was associated with vulval and vaginal cancers, so that's very exciting," said Dr. Leo Twiggs, professor and chairman of the department of obstetrics and gynecology at the University of Miami Miller School of Medicine. "It's the answer to whether the cause is HPV."

The findings appear in the May 19 issue of The Lancet; initial data was first presented at the American Society of Clinical Oncology meeting last year.

Although less common than cervical cancer, vulval and vaginal cancers are becoming more widespread in young women. The incidence of in situ vulval carcinoma increased more than 400 percent in the United States between 1973 and 2000. Invasive vulval cancer increased by 20 percent during the same period.

The Gardasil vaccine was developed to target four strains of HPV, two of which (HPV 16 and 18) are linked to cervical cancer and to vulval cancer, and two (HPV 6 and 11) which cause anogenital warts.

Unlike cervical cancer, there are no screening programs for vaginal or vulval cancer.

Recent research also found that HPV is probably the number one cause of throat cancer, which affects about 11,000 Americans each year.

The HPV vaccine has already been shown to be almost 100 percent effective in preventing HPV 16-related or HPV 18-related cervical lesions, which are precursors to cancer.

Here, the authors did a combined analysis of three randomized clinical trials involving, collectively, more than 18,000 women aged 16 to 26 in 24 countries around the world. The research was funded by Merck, which makes Gardasil.

Participants had been randomly assigned to receive either the vaccine or a placebo.

After three years of follow-up, the vaccine proved to be 100 percent effective against vulval and vaginal lesions related to HPV 16 or HPV 18 in women never previously exposed to the HPV virus. The vaccine was 71 percent effective in women previously exposed to HPV.

The vaccine reduced the risk of high-grade vaginal and vulval lesions by 49 percent, regardless of whether HPV was detected in the lesion.

"This is very impressive," said Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System in Baton Rouge, La. "We're having a paradigm shift. It's very hard for a lot of people to recognize that we can actually prevent cancer, and it's very hard for people to recognize that certain types of cancer are sexually transmitted. The vaccine is very good. It is not perfect. It does not protect against every viral infection from HPV, but it protects against the ones that are the most common."

According to the Finnish study authors, the maximum effect of the vaccine would be expected in girls who are vaccinated in early adolescence, before any exposure to HPV.

"I would recommend it for my daughters and anybody else's daughters," Brooks said.

"I've been practicing medicine for 30 years and have seen patients die of cervical cancer and oftentimes younger patients who have kids at home," Twiggs added. "It's great that we can actually prevent it. It's very important for us to get the word out there about how this could prevent cancer."